A typical vehicle wheel tire has a tire tread having tread grooves. When such a tire is rolling on the ground, the portion of the tire tread on and adjacent its ground contacting area is subject to deformation, which in turn causes deformation of the tread grooves so as to generate stresses and strains in the bottom and side walls of the tread grooves. In particular, those tires that have to bear relatively heavy loads, such as the tires for trucks and buses, may often experience cracks produced in the bottom walls of the tread grooves due to relatively large deformation of the grooves caused by such excessive loads. In order to prevent the tires from the damage caused by the cracks in the bottom walls of the tread grooves, it is important to configure the shape of the tread grooves such that the grooves have no site of strain concentration. For this purpose, it is desired to make precise measurements of deformation, and in particular of the deformed shape and/or the stress distribution, of the tire tread of a tire under the condition where the tire is subject to such deformation that is similar to that experienced when the tire is in actual use, i.e., when the tire tread is in contact with the ground surface with a certain load applied to the tire.
There have been proposed several precision measurement techniques for measuring the shape of a tire tread. Some of such known techniques use a laser triangulation unit to carry out non-contact precision measurement of the three-dimensional shape of a tire tread. An example of such techniques is described in Japanese Published Patent Application No. 2007-132807.
This and other known techniques, however, measure the shape of a tire tread when it is not in contact with any surface, and thus is not subject to deformation which could be produced under actual use conditions of the tire.
Under the circumstances, it is an object of the present invention to provide a method for measuring deformation of a tire tread, in which the deformation is similar to that experienced when the tire is in actual use and thus when the tire tread is in contact with the ground surface.